1. Field of the Invention
The present invention relates to a computer program product, system, and method for pre-allocating storage space for an application operation in a space efficient volume.
2. Description of the Related Art
In a storage environment, a storage controller may create point-in-time (“PiT”) copies of a production volume using point-in-time copy techniques, such as the IBM FlashCopy® (FlashCopy is a registered trademark of IBM), snapshot, etc. A point-in-time copy replicates data in a manner that appears instantaneous and allows a host to continue accessing the source volume while actual data transfers to the copy volume are deferred to a later time. The point-in-time copy appears instantaneous because Input/Output (“I/O”) complete is returned to the copy operation in response to generating the relationship data structures without copying the data from the source to the target volumes. Point-in-time copy techniques typically defer the transfer of the data in the source volume at the time the point-in-time copy relationship was established to the copy target volume until a write operation is requested to that data block on the source volume. Data transfers may also proceed as a background copy process with minimal impact on system performance. The point-in-time copy relationships that are immediately established in response to the point-in-time copy command include a bitmap or other data structure indicating the location of blocks in the volume at either the source volume or the copy volume. The point-in-time copy comprises the combination of the data in the source volume and the data to be overwritten by the updates transferred to the target volume.
In a space efficient volume, volumes are thinly provisioned which means that physical storage space is not allocated to the volumes until a write to the volumes requires the space. The amount of space that is allocated is based on the amount of data that is written to the volume. In space efficient volumes, the device capacity for the devices assigned to the repository pool exceeds the physical addresses allocated to the volumes.
In space efficient volumes, when a point-in-time copy operation is performed, physical storage space is allocated only when a write operation is performed as part of the copying of the point-in-time data from the source storage to the target storage so that data is allocated to the target storage when needed for a specific transfer that is occurring.